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Robust Benzimidazole-based Electrolyte Overcomes High-voltage and High-temperature Applications in 5 V Class Lithium Ion Batteries
F.-M. Wang*, S. A. Pradanawati, N.-H. Yeh, S.-C. Chang, Y.-T. Yang, S.-H. Huang, P.-L. Lin, J.-F. Lee, H.-S. Sheu, M.-L. Lu, C.-K. Chang, A. Ramar, and C.-H. Su
Electric vehicles (EVs) are poised to dominate the next generation of transportation, but meeting the power requirements of EVs with lithium ion batteries is challenging because electrolytes containing LiPF6 and carbonates do not perform well at high temperatures and voltages. However, lithium benzimidazole salt is a promising electrolyte additive that can stabilize LiPF6 through a Lewis acid–base reaction. The imidazole ring is not eligible for high-voltage applications owing to its resonance structure, but in this research, electron-withdrawing (−CF3) and electron-donating (−CH3) substitutions on imidazole rings were investigated. According to the calculation results, the CF3 substitution facilitates a high electron cloud density on imidazole ring structures to resist the electron releases from bezimidazole in oxidation reactions. In addition, through CF3 substitution, electrons are accepted from the lattice oxygen (O2–) in lithium-rich layer material and O– is converted by an electron released. The O– is then adsorbed with the ethylene carbonate and catalyzed to alkyl carbonate by Ni2+. The −CF3 substituted benzimidazole triggers a further reaction with alkyl carbonate and forms a new polyionic liquid solid electrolyte interphase on the cathode’s surface. Furthermore, the cycle performance tested at 60 °C and 4.8 V showed that the CF3 substitution maintains the battery retention effectively and exhibits almost no fading compared with both the blank electrolyte and the CH3 substitution.